The present invention relates generally to techniques for issuing device requests in a computer system. More particularly, the present invention relates to a system in which a device may issue a device request on behalf of another device.
Connectivity between disparate devices within a computer system or between modules in an integrated circuit or ASIC is often accomplished through at least one central switch that is connected to devices on different busses throughout the system. A central switch allows transactions to be routed internally, so that each device is able to access other modules connected to the central switch, without requiring additional ports or unnecessary logic specific to the target resource or target device. For example, a memory control module in a system controller having a central switch may be accessed through this central switch from the interface for the system processor, from a number of busses within the computer system, or perhaps from other devices or modules within the system controller. In order to communicate with this memory control module, other devices connected to the switch only need to communicate with the central switch, which translates requests from the form appropriate for one device to a form suitable for another.
When a request is issued by one device to another, the device that is the source of the request includes two request two tags within the request. These two tags identify the source device for the request and the destination device for the request. When a device issues a request to another device, the source or requesting device issues a request to the central switch, identifying itself as the source, and the target device as the destination. The switch then analyzes the tags, performs any necessary translation, and then communicates the request to the target or destination device as identified by the destination tag. Thereafter, the requested operation is performed.
Often the conventional procedure of issuing device requests in such an environment works efficiently. However, in some situations, inefficiencies or redundancies result when the requesting device identifies itself to the switch as the source. These inefficiencies result in increased loads on the central switch, and also in unnecessary demands on some of the devices or other resources within the system. Thus, there exists a need for an efficient system and method for more efficiently issuing requests between devices in a computer system, while also maintaining compatibility with applicable bus standards or other standards, and while not unnecessarily increasing the complexity of devices within the system.
The present invention relates to techniques for issuing device requests by proxy. In one embodiment of the invention, the invention relates to a computer comprising: (a) a bus; (b) a system controller connected to the bus so that it can access devices on the bus, wherein the system controller comprises a switch that receives requests identifying a source device and a destination device, wherein the switch routes each request to a destination device identified by the request; and (c) a proxy device that is attached to the switch, and that sends a request to the switch identifying a destination device and a source device, wherein the source device is a device that is different from the proxy device.
In another embodiment of the present invention, the present invention relates to a computer comprising: (a) a processor connected to a host bus; (b) system memory connected to a memory bus; (c) a device connected to an expansion bus; and (d) a system controller connected to the host bus, the memory bus, and the expansion bus so that it can access devices on the host bus, the memory bus, and the expansion bus. The system controller comprises: (i) a switch that receives requests identifying a source device and a destination device, wherein the switch routes the requests to the identified destination device, and (ii) a proxy device that is attached to the system controller and that sends a request to the switch identifying a destination device and a source device, wherein the source device is a device that is different than the proxy device.
Additional embodiments and features, and the nature of the present invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims, and to the several drawings herein.